Various golf balls, golf ball layers, and methods of making golf balls are known in the art. Generally, golf balls have been classified as two piece balls or three piece balls. Two piece balls are comprised of a solid polymeric core and a cover. Two piece balls are generally easy to manufacture, but are regarded as having limited playing characteristics. Three piece balls are comprised of a solid or liquid-filled center surrounded by tensioned elastomeric material and a cover. Three piece balls generally have good “feel” when struck by a golf club, but are more difficult to manufacture than two piece balls.
The prior art is comprised of various golf balls that have been designed to optimize playing characteristics. These characteristics are generally the initial velocity and spin of the golf ball. For instance, certain players prefer to play a ball that has a high spin rate for playability. Other players prefer to play a ball that has a low spin rate to maximize distance. Therefore, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers that demand varied playing characteristics.
Golf balls are presently formed from a variety of materials depending upon the performance characteristics desired. One of the softest materials conventionally used to form golf ball covers is balata, which is the trans-isomer form of the 1,4-chain polymer of isoprene. For many years, balata was the standard cover stock material used in forming most golf balls. Balata covered balls were favored among professionals and more advanced amateur players until recently because the softness of the cover allows the player to achieve spin rates sufficient to precisely control ball direction and distance, particularly on shorter approach shots.
Because of its softness, however, balata is susceptible to cuts or other damage to the cover resulting from a mis-hit shot. Accordingly, harder, more durable cover materials, e.g., ionomer resins such as SURLYN®, have been developed that provide higher durability, but less spin and feel, than balata balls. Resins such as SURLYN® are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as lithium, zinc, or sodium, are used to neutralize some portion of the acidic groups in the copolymer resulting in a thermoplastic elastomer for use as a golf ball cover. Additionally, various softening comonomers, such as n-butyl acrylate, may be added during the ionomer manufacturing process to improve golf ball performance characteristics, such as spin and feel. In the early 1980s, low modulus SURLYN® ionomers were introduced and subsequently utilized to impart more spin and an improved, balata-like feel to golf balls.
Golf balls may be provided with a coating of one or more layers to protect the cover. Golf balls must be capable of withstanding a variety of weather conditions, such as strong sunlight, extreme temperature ranges, and immersion in water, preferably for an extended period. Further, the surface of a golf ball is flexed due to the impact every time it is struck with a club and, consequently, these surfaces must be able to withstand such repeated stresses. Moreover, especially with the recreational player, golf balls are susceptible to striking any of a number of hard, abrasive surfaces, such as concrete, asphalt, brick, stone, etc., as a result of errant shots. It is therefore desirable for golf ball manufacturers that their golf balls be resistant to delamination or chipping of the coating layers, as such defects impact negatively upon the public perception of the quality of the golf ball.
Likewise, golf ball manufacturers also seek to prevent obliteration of all or part of their trademarks, logos, or other identifying indicia that identifies the brand of the ball to the playing public. Protective coatings are therefore applied to the surface of the golf ball cover. A clear primer coat and top coat layer are commonly applied to the cover to provide a high gloss and an overall enhanced appearance to the ball. In such coated balls, the various identifying indicia may be applied either to the cover, the primer coat, or the topcoat.
Protective and decorative coating materials, as well as methods of applying such materials to the surface of golf ball covers, are well known in the golf ball art. Generally, such coating materials comprise urethanes, urethane hybrids, polyesters, and acrylics. If desired, more than one coating layer may be used. Typical two pack polyurethane coatings include separate packages of polyol and diisocyanate. Conventionally, a primer layer, such as a solvent-based or a water-based polymer, may be applied to promote adhesion or to smooth surface roughness before the finish coat(s) are deposited on the golf ball. In general, a cured polyurethane-based top coat is most widely used as a protective coating material.
U.S. Pat. No. 5,749,796 discloses a wound golf ball having a resin film as a second cover layer that is disposed about the first cover layer, the second cover layer having a thickness of less than 300 microns
U.S. Pat. No. 5,997,417 discloses a golf ball having an in-mold coating with a substantially uniform thickness of about 0.05 to 100 mils, the coating being applied to a dimpled cover.
U.S. Pat. No. 5,836,833 discloses a golf ball having an outer cover layer of ionomer, polyurethane, or ethylene vinyl acetate, having a thickness of 0.01 to 0.05 mm and a Shore D hardness of 48 to 55, and an inner cover layer having a thickness of 1.2 to 4.0 mm and a Shore D hardness of 58 to 70.
U.S. Pat. No. 6,068,561 discloses a golf ball with a multi-piece cover having at least three layers, each layer having a different hardness and a thickness of about 0.01 to 0.03 inches.
Japanese Patent No. 61-112619 discloses a wound multilayer golf ball having a protective thermoplastic layer having a thickness of 10 to 500 microns.
The varied composition and manufacturing of other portions of golf balls is also well known in the art.
Both U.S. Pat. Nos. 1,568,513 and 1,904,012 are directed to wound golf balls with liquid filled centers.
U.S. Pat. Nos. 5,150,906 and 5,480,155, are directed to as hollow spherical shell of a polymeric material which is filled with a liquid or unitary, non-cellular material that is a liquid when introduced into the shell. The shell is disclosed as being the outer cover or an inner layer with the outer cover formed to the external surface thereof. The shell varies in thickness from about 1.52 to 10.41 mm in thickness.
U.S. Pat. No. 6,132,544 discloses a method of molding a solid golf ball including disposing a core between two ionomer resin films and heat pressing the films to the wrapped ball body in a dimpling mold to form the cover.
U.S. Pat. No. 5,730,665 discloses a three-piece golf ball, wherein the intermediate layer and the outermost layer of formed of a laminate film made from a material that is smoothly releasable from the mold. The intermediate layer has a thickness of 50 to 400 microns and the outermost layer has a thickness of 5 to 100 microns.
Particularly with respect to polyurethane-containing materials golf balls can be currently made by casting or injection molding processes. The nature of current casting processes is such that materials that require a relatively long time (in comparison to other fabrication methods) to sufficiently solidify, i.e., react thoroughly. As a result, materials or compounds with particular chemistries that react or solidify relatively quickly are generally restricted from use in commercial casting processes, particularly in the golf art.
By using an alternative fabrication technique, reaction injection molding, as opposed to traditional injection molding, thermosetting materials and/or materials with relatively quick reaction or solidification times can be processed. Reaction injection molding processes, due to the nature of the chemistries of the materials used, tend to result in decreased fabrication times, and can facilitate a decrease in the cost of fabricating such articles. The technique of reaction injection molding using a variety of materials has been demonstrated in various publications.
Reaction injection molding has been disclosed in International Publication No. WO 00/57962, which claims golf balls, and processes for making such balls, comprising a reaction injection molded material, such as polyurethanes/polyureas.
In addition, U.S. Pat. No. 6,083,119 discloses a multi-layer golf ball with an inner and outer cover layer, at least one of which can contain a reaction injection molded polyurethane material.
U.S. Pat. Nos. 4,695,055 and 4,878,674 also disclose illuminated, translucent golf balls having a permanent diametric hole into which a chemiluminescent light stick is added, so that the golf balls may be visible in the dark. These golf balls can be fabricated by a method such as reaction injection molding.
Until recently, compounds that can be cured in to urethanes, such as isocyanates and hydroxyl-containing polymers, had to be stored separately and were mixed at the time of their use. However, chemically modifying, “blocking” or “masking,” the reactive substances now permits one-part curable compositions.
U.S. Pat. No. 6,221,998 discloses an isocyanate-based one-part moisture curable composition having excellent storage stability and high curing rate. The composition comprises an isocyanate and a ketimine that are chemically blocked so that the initiation of curing can be controlled.
U.S. Pat. No. 6,166,164 discloses blocked polyisocyanates with a high latent isocyanate content used for the production of heat-curable polyurethane polymer coating systems.